Heat exchanger with flat tubes

ABSTRACT

A heat exchanger including first and second header tanks for receiving and discharging refrigerant. Further, the first and second header tanks are spaced apart from each other by a predetermined distance. Also include is a plurality of flat tubes each having opposite ends respectively connected to the first and second header tanks, in which each of the flat tubes has channels through which the refrigerant scatters and flows, and the channels have a different capacity from each other. Further included is a cooling member for discharging heat of the refrigerant flowing along the flat tubes.

This Non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No(s). 10-2003-0061858 filed in Korea onSep. 4, 2003, the entire contents of which are hereby incorporated byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a heat exchanger with flat tubes, andmore particularly, to a heat exchanger with flat tubes that can improvethe heat exchange efficiency by making capacities of channels of eachflat tube different from each other.

2. Description of the Related Art

Generally, an air conditioner for cooling interior air using a coolingcycle includes a compressor for compressing refrigerant to a highpressure, a condenser for exchanging heat of the compressed refrigerantwith exterior air to liquefy refrigerant gas, and an evaporator forexchanging heat of the liquefied refrigerant with the interior air usingan expansion valve or capillary tubes to evaporate the liquefiedrefrigerant. The air conditioner performs the cooling operation by usingheat of gasification of refrigerant.

Thus, the air conditioner is configured to control the temperature of anenclosed space by inducing a phase transition of the refrigerant using aheat exchanger such as the condenser and the evaporator. Therefore, inorder to improve the cooling efficiency, it is very important to improvethe efficiency of the heat exchanger.

Due to the above reasons, in recent years, there appears a super compactcondenser (SCC), which is designed to dramatically improve theheat-exchange efficiency by arranging a plurality of flat tubes in azigzag-shape to allow the refrigerant to simultaneously flow. FIG. 1shows a conventional heat exchanger with flat tubes used to perform heatexchange in an air conditioner using refrigerant.

Referring to FIG. 1, a heat exchanger with flat tubes includes first andsecond header tanks 10 and 20 disposed in parallel and spaced apart fromeach other at a predetermined distance, a plurality of refrigerant tubes12 disposed in parallel and spaced apart from each other at apredetermined distance, opposite ends of each refrigerant tube 12 areconfigured to communicate with the first and second header tanks 10 and20, respectively, and a plurality of cooling fins 14 formed on therefrigerant tubes 12 to discharge heat of the refrigerant flowing alongthe refrigerant tubes 12.

The first and second header tanks 10 and 20 are disposed facing eachother, and refrigerant inlet and outlet tubes 16 and 18 are respectivelyconnected to the first and second header tanks 10 and 20. In addition,at least one refrigerant separation membrane for directing refrigerantin a desired direction is disposed in the first and second header thanks10 and 20.

In operation, the refrigerant introduced into the first header tank 10through the refrigerant inlet tube 16 flow into the second header tank20 along the refrigerant tubes 12 connecting the first header tank 10 tothe second header tank

The refrigerant reciprocally flow between the first and second headertanks 10 and 20 by the separation membranes 22 disposed in the first andsecond header tanks 10 and 20, and are then discharged through therefrigerant outlet tube 18 of the second header tank 20 after repeatedlymoved between the first and second header tanks 10 and 20. At thispoint, the refrigerant generate heat in the course of flowing along therefrigerant tubes 12, and the generated heat is radiated through thecooling fins 14 surface-contacting the refrigerant tubes 12. Since theheat exchanger is used as an evaporator or a condenser, it can functionto increase or decrease the temperature of interior air.

FIG. 2 shows a sectional view taken along the line A–A′ of FIG. 1.

Referring to FIG. 2, the tube 12 is formed in a flat shape having asectional structure in which refrigerant-flowing holes 12 a ofmulti-channels Ch1–Chn are formed. Such a flat tube 12 is generallyemployed to a heat exchanger used as a high efficiency condenser.

The refrigerant is dispersed and flows along the refrigerant-flowingholes 12 a configured in the multi-channels Ch1–Chn by a small amount.At this point, the dispersed refrigerant uniformly contacts an entireinner circumference of the respective refrigerant-flowing holes 12 a bysurface tension, so that an annular flow phenomenon is generated toincrease the heat transfer efficiency. In addition, since an amount ofthe pressure drop is small, the flow of the refrigerant can be morestably realized.

Also, the refrigerant flowing along the header tanks 10 and 20 transfersheat through the cooling fins 14 surface-contacting an outercircumferences of the tubes 12 while passing through the multi-channelsCh1–Chn, i.e., the refrigerant flow holes 12 a, thereby increasing ordecreasing the air temperature.

Meanwhile, as described above, the refrigerant flow holes 12 a of theflat tube are formed in a kind of the micro multi-channels Ch1, Ch2, . .. , Chn. Each of the channels has a rectangular section with anidentical width. In addition, each of the foremost and rearmost channelsCh1 and Chn has a hemispherical outer end section to reduce the contactresistance with the air.

However, since the widths of channels are identical to each other andthe intervals between the channels are also identical, it is difficultto maximize the heat transfer efficiency at a front end portion of thetube, thereby deteriorating the heat transfer efficiency of the heatexchanger.

SUMMARY OF THE INVENTION

Accordingly, the present invention is directed to a heat exchanger withflat tubes that substantially obviates one or more problems due tolimitations and disadvantages of the related art.

A first object of the present invention is to provide a heat exchangerwith flat tubes each having multiple channels that have differentrefrigerant flow capacities from each other.

A second object of the present invention is to provide a heat exchangerwith flat tubes each having multiple channels, in which the capacitiesof the multi-channels are increased or decreased at a predetermined rateaccording to a direction where exterior air flows.

A third object of the present invention is to provide a heat exchangerwith flat tubes each having multi-channels, in which widths of themulti-channels are designed to increase or decrease a refrigerant flowcapacity in response to a flow capacity of exterior air.

A fourth object of the present invention is to provide a heat exchangerwith flat tubes each having multiple channels, in which a width of aforemost channel among the channels is broadest and a width of arearmost channel among the channels is narrowest.

A fifth object of the present invention is to provide a heat exchangerwith flat tubes each having multiple channels, in which adjacentchannels among the channels have different widths.

A sixth object of the present invention is to provide a heat exchangerwith flat tubes each having multiple channels, in which widths of thechannels are decreased at a predetermined rate in a direction whereexterior air flows.

A seventh object of the present invention is to provide a heat exchangerwith flat tubes each having multiple channels each channel beingprovided at an inner circumference with a plurality of grooves.

An eighth object of the present invention is to provide a heat exchangerwith flat tubes each provided at portions that do not contact coolingfins with ridge-shaped projections.

Additional advantages, objects, and features of the invention will beset forth in part in the description which follows and in part willbecome apparent to those having ordinary skill in the art uponexamination of the following or may be learned from practice of theinvention. The objectives and other advantages of the invention may berealized and attained by the structure particularly pointed out in thewritten description and claims hereof as well as the appended drawings.

To achieve these objects and other advantages and in accordance with thepurpose of the invention, as embodied and broadly described herein,there is provided a heat exchanger comprising: first and second headertanks through which refrigerant is introduced and discharged, the firstand second header tanks being spaced apart from each other by apredetermined distance; a plurality of flat refrigerant tubes eachhaving opposite ends respectively connected to the first and secondheader tanks, each of the refrigerant tubes having channels throughwhich the refrigerant scatter and flow, the channels having a differentcapacity from each other, the first and second header tankscommunicating with each other through the channels; and cooling meansdisposed between the refrigerant tubes, for radiating heat of therefrigerant flowing along the tubes.

Preferably, each of the refrigerant tubes comprises a refrigerant flowhole of a multi-channel structure having at least two different channelcapacities to allow the refrigerant to scatter and flow.

Preferably, intervals between the channels are different from eachother.

Preferably, among the channels, a first channel formed on a front end ofeach of the refrigerant tubes, has a biggest channel capacity, and ann-th channel formed on a rear end of each of the flat tubes has asmallest channel capacity, when the order of the first and the n-th isreferenced by the air flow direction.

Preferably, the channel capacities of the refrigerant tubes aregradually decreased at a predetermined rate as it goes from a firstchannel formed on a front end of the refrigerant tube to an n-th channelformed on a rear end of the refrigerant tube.

Preferably, adjacent channels of each of the refrigerant tubes have adifference in their capacities and widths by a predeterminedreduction/increase rate.

In another aspect of the present invention, there is provided a heatexchanger comprising: first and second header tanks through whichrefrigerant is introduced and discharged, the first and second headertanks being arranged spaced apart from each other by a predetermineddistance; a plurality of flat refrigerant tubes arranged spaced awayfrom one another by a predetermined distance and connected between thefirst and second header tanks, for dispersing and flowing refrigerant,each of the refrigerant tubes having a multi-channel structure in whicha first channel, which is formed on a front end of each tube and firstcontacts air, has a biggest channel capacity, and an n-th channel, whichis formed on a rear end of each tube, has a smallest channel capacity;and cooling fins disposed between the refrigerant tubes for heatdischarge.

In another aspect of the present invention, there is provided a heatexchanger comprising: first and second header tanks through whichrefrigerant is introduced and discharged, the first and second headertanks being arranged spaced apart from each other by a predetermineddistance; a plurality of flat refrigerant tubes each havingmulti-channels of which widths are gradually reduced by a predeterminedreduction ratio as it goes in a direction where exterior air flows, therefrigerant tubes flowing refrigerant between the pair of header tanksthrough the multi-channels; and cooling fins disposed between therefrigerant tubes for heat discharge.

It is to be understood that both the foregoing general description andthe following detailed description of the present invention areexemplary and explanatory and are intended to provide furtherexplanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiment(s) of the invention andtogether with the description serve to explain the principle of theinvention. In the drawings:

FIG. 1 is a front view of a conventional heat exchanger with flat tubes;

FIG. 2 is a sectional view taken along the line A–A′ of FIG. 1;

FIG. 3 is a perspective view of a heat exchanger with flat tubesaccording to an embodiment of the present invention;

FIG. 4 is a sectional view taken along the line B–B′ of FIG. 3;

FIG. 5 is a sectional view of a modified example of a flat tube depictedin FIG. 3;

FIG. 6 is a graph illustrating a variation of a heat transfer rate inaccordance with regions of a heat exchanger;

FIG. 7 is a view illustrating various examples of a refrigerant flowhole formed in a flat tube according to another embodiment of thepresent invention;

FIG. 8 a is a perspective view of a flat tubes/fins assembly accordingto another embodiment of the present invention;

FIG. 8 b is a sectional view taken along the line C–C′ of FIG. 8 a; and

FIG. 9 is a front view of a heat exchanger where the flat tubes/finsassembly depicted in FIG. 8 a is employed.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the preferred embodiments of thepresent invention, examples of which are illustrated in the accompanyingdrawings. Wherever possible, the same reference numbers will be usedthroughout the drawings to refer to the same or like parts.

FIG. 3 shows a perspective view of a heat exchanger with flat tubesaccording to an embodiment of the present invention.

As shown in FIG. 3, the inventive heat exchanger includes: first andsecond header tanks 110 and 120; a plurality of flat tubes 112 arrangedin parallel and spaced apart from each other at an identical distancebetween the first and second header tanks 110 and 120, each of the flattubes 112 having a plurality of refrigerant flow holes 112 a defined bya plurality of channels Ch1–Chn having different capacities from eachother to allow refrigerant to disperse and flow to the first and secondheader tanks 10 and 20; and cooling fins 114 disposed between the flattubes 112 to radiate heat.

The first and second header tanks 110 and 120 are respectively connectedto refrigerant inlet and outlet tubes 116 and 118. Each of the first andsecond header tanks 110 and 120 has therein one or more refrigerantseparating membranes 122 for directing the refrigerant in a desireddirection.

Next, operation and effects of the flat tube type heat exchangerconstructed as above will be described with reference to theaccompanying drawings.

Referring to FIGS. 3 and 4, the first and second header tanks 110 and120 are arranged in parallel spaced apart from each other by apredetermined interval, and receive the refrigerant introduced throughthe refrigerant inlet tube 116. The received refrigerant flows throughthe tubes 112, is induced in a predetermined direction by therefrigerant separating membranes 122, and is then discharged through therefrigerant outlet tube 118.

The cooling fins 114 are disposed in a bellows shape inclined with apredetermined angle between the flat tubes 112 communicating the firstand second header tanks 110 and 120 with each other.

The flat tube 112 is designed to allow the refrigerant to disperse andflow through the refrigerant flow holes 112 a defined by the multiplechannels Ch1–Chn. The 114 cooling fins surface-contact the outersurfaces of the tubes 112 and are inclined at a predetermined angle45–90° to enlarge the cooling area.

Therefore, the tubes have a heat exchange capacity that is in proportionto an inner contacting area defined by the channels Ch1–Chn contactingthe refrigerant, an outer contacting area defined by the cooling fins114, and a flow capacity of the exterior air.

At this point, the tubes 112 affect the flow capacity of the refrigerantand the heat transfer in proportion to the channel capacity and thecontact area. That is, the more the channel capacity (W X H) and therefrigerant contacting area, the higher the heat transfer efficiency.

In a modified example of the present invention, the channels Ch1–Chn ofeach tube 112 have different channel capacities or different channelwidths from each other. As an example, it is preferable that thechannels Ch1–Chn are formed with at least two different channelcapacities or at least two different channel widths.

In addition, the first channel Ch1 that is located on a front end Ft ofthe tube 112 is designed having a widest width (W1), and the lastchannel Chn that is located on a rear end Rt of the tube 112 is designedhaving a narrowest width (Wn) so that the last channel has a smallestchannel capacity.

That is, since the exterior air is introduced into the first channel Ch1and discharged through the last channel Chn, the first channel Ch1 thatfirst contact the exterior air is designed having the highestrefrigerant flow capacity in proportion to the heat transfer rate andthe channel capacity, and the last channel Chn that lastly contact theexterior air is designed having the lowest refrigerant flow capacity.

Alternatively, all of the channels Ch1–Chn of each of the tubes 112 havedifferent channel widths W1–Wn from each other. Preferably, the channelwidths W1–Wn of the first to last channels Ch1–Chn that are arranged inthis order in a direction where the interior air flows are graduallyreduced at a predetermined rate as they go toward the air dischargedirection. That is, intervals between the channels are graduallyreduced.

In other words, when assuming that a channel, which is located on afront end Ft of the tube 112 and first contacts exterior air, a is firstchannel (Ch1), a channel, which is adjacent to the first channel (Ch1),is a second channel, and a channel, which is located on a rear end, isan n-channel, a width W1 of the first channel Ch1 is greater than thatof the second channel Ch2 by a predetermined length. The widths ofadjacent channels can be adjusted at an identical reduction rate. Forexample, a reduction ratio of the width (W2) of the second channel tothe width (W1) of the first channel may be set to 6% or 10%. In otherwords, the widths W1–Wn of the first to last channels Ch1–Chn may begradually reduced at a reduction rate of 6% or 10%.

That is, as shown in FIG. 3, when the width reduction rate is set to 6%,the width W2 of the second channel Ch2 is less than that W1 of the firstchannel Ch1 by 6%, the width W3 of the third channel Ch3 is less thanthat W2 of the second channel Ch2 by 6%, . . . , and the width Wn-1 ofthe channel Chn-1 is less than that Wn of the last channel Chn by 6%.Therefore, the relationship of the widths W1 and Wn of the respectivefirst and last channels Ch1 and Chn become W1>>Wn.

Likewise, as shown in FIG. 4, the flat tubes 112 (112-1, 112-2, 112-3, .. . , 112-n) arranged in parallel at a constant interval are designedsuch that the channels having an identical channel number have anidentical channel width (W) and the channels having different channelnumbers have different channel widths, and the width of all the channelsis reduced at a constant rate according to the order of the channels(Ch1, Ch2, . . . Chn). In a modified example, the outermost tubes (theuppermost and lowermost tubes) can be designed to be different in theirwidth from the tubes located at a center portion of the heat exchanger.That is, some channels located at the center portion are designed as inFIG. 3, and the channels of the outermost tubes are designed as in theconventional art.

FIG. 5 shows a modified example of the flat tube according to thepresent invention.

In this modified example, the width reduction rate is set to 10%. Thatis, the width W2 of the second channel Ch2 is less than that W1 of thefirst channel Ch1 by 10%, the width W3 of the third channel Ch3 is lessthan that W2 of the second channel Ch2 by 10%, . . . , and the width Wnof the last channel Chn is less than that Wn-1 of the channel Chn-1 by10%. Therefore, the relationship of the widths W1 and Wn of therespective first and last channels Ch1 and Chn become W1>>Wn.

This modified example shows that the width reduction rate is set in arange of about 6–10% in proportional to a flow rate of exterior air anda flow rate of the refrigerant. On the contrary, the widths of theadjacent front and rear channels in the first to last channels may beset at a width increase rate of 6–10%.

Alternatively, the tubes may be configured such that the channelsCh1–Chn are grouped into two or three groups, and the widths of thegroups are set to be different from each other.

Alternatively, the tubes may be configured such that the width W1 of thefirst channel Ch1 is necessarily greater than the width Wn of the lastchannel Chn, and the ratio of the widths of adjacent two channels exceptfor the first and last channels Ch1 and Chn is identical or different toor from each other. In addition, even though the width reduction rate orwidth increase rate of the channels in the tubes 112 (or 122) isadjusted, the sum of the sectional areas of the multiple channelsCh1–Chn may be identical to that of the conventional art.

The width reduction or increase rate (ex. 6–10%) of the channels Ch1–Chnis determined depending on a heat transfer amount at the front end 112 b(or 122 b) of the tubes 112 (or 122) or an expected heat transferefficiency. Alternatively, by varying a ratio of heights H of thechannels, it is also possible to improve the heat transfer efficiency.Alternatively, by varying ratios of the heights H and widths W, it isalso possible to improve the heat transfer efficiency.

FIG. 6 shows a graph illustrating a variation of a heat transfer rate atthe tube of the present invention. As shown in FIG. 6, the heat transferamount is largest at the front end Ft of the tube that first contactsthe air and is then gradually reduced as it goes to the rear end Rt ofthe tube. That is, in the fin-tube-type heat exchanger, the heattransfer amount in the front end Ft of the tube is about 80% of anamount of overall heat transfer of the heat exchanger. Accordingly, bymaking the width W1 of the first channel Ch1 located on the front end Ftof the tube where the heat exchange is most active to be widest so thata large amount of refrigerant can flow along the first channel Ch1, anamount of overall heat transfer can be increased.

In addition, even though the sectional areas of the channels aredifferent from each other, if the walls between the channels aredesigned having an identical thickness to each other, the sum of thesectional areas of the channels becomes identical to that of channelsdesigned having an identical sectional area to each other.Alternatively, the widths of the channels located on the front side ofeach tube may be different depending on air contact amount.

FIG. 7 shows various examples of a refrigerant flow hole formed in aflat tube according to another embodiment of the present invention;

As shown in (a) to (d) of FIG. 7, an inner circumference of arefrigerant flow hole 132 a, 142 b, 152 c or 162 d formed in the tube132, 142, 152 or 162 is formed in a variety of sectional shapes such asa groove, an irregular surface, or a parabola. In other words, in themodified examples of FIGS. 7( a) to 7(d) having a plurality of groovesas to increase the contact area with the refrigerant, thereby improvingthe heat discharge efficiency.

FIGS. 8 a, 8 b and 9 show another embodiment of the present invention.

Referring first FIGS. 8 a and 8 b, each of tubes 172 is provided atportions of its outer surface, which do not contact cooling fins 174,with a plurality of riblets 175 arranged in parallel in a directionwhere air flows. Therefore, the heat exchange between refrigerantflowing along the tube and exterior air can be increased by the riblets175 as well as the cooling fins 174 as shown in FIG. 9.

That is, the cooling fins 174 are vertically disposed between the tubes172 at a predetermined inclined angle, and the riblets 175 areintegrally formed on portions of the outer surface of the tube, which donot contact cooling fins 174. A section of each riblet 175 is formed ina ridge-shape or a triangular-shape to (a) increase the contact areawith the exterior air, (b) reduce the pressure drop, and (c) enhance theair flow rate.

As described above, the cooling fins 174, the riblets 175, and themulti-channels Ch1–Chn function to increase contact area, to maximizethe heat transfer efficiency and to minimize the pressure drop.

In FIG. 9, a heat exchanger is shown in which heat radiating means 174,175 having different shapes and materials are formed on tubes 172connected between a pair of header tanks 170 and 171.

According to the above described modified example, since the innercircumference of the tube is designed having heat radiating means shapedin a groove and the outer surface of the tube is designed having heatradiating means including cooling fins and riblets, and the heatradiating means are integrated, an overall contact area of the heatexchanger is increased to thereby maximize the heat transfer efficiency.

In addition, since the channels formed in the tube are designed havingdifferent width ratio and height ratio from each other in response toair flow capacity, it is possible to increase heat transfer rate.

As described previously, according to the present invention, capacitiesof channels of a tube are formed different according to the flow rate ofexterior air and air contact amount so that refrigerant flow rate andheat transfer rate in a heat exchanger are increased.

Also, among the channels of a refrigerant tube, a first channel, whichmost frequently contacts exterior air, is designed having the greatestwidth and an n-th channel, which least frequently contacts exterior air,is designed having the smallest width so that it is possible to increaserefrigerant flow rate according to flow rate of exterior air.

In addition, the refrigerant tube is designed having a channel capacityor a channel width, which is reduced from the front end to the rear endby a constant reduction rate of 6–10% so that it is possible to increasea heat transfer amount at a local portion of the refrigerant tub or atotal heat transfer amount.

Further, the inner circumference of the channels of the refrigerant tubeis designed having grooves and the outer surface of the tube is designedhaving riblets so that the contact area of the heat exchanger withrefrigerant is increased to thereby maximize the heat transferefficiency, increase exterior air contact area and reduce the pressureloss.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the present invention. Thus,it is intended that the present invention covers the modifications andvariations of this invention provided they come within the scope of theappended claims and their equivalents.

1. A heat exchanger comprising: first and second header tanks throughwhich refrigerant is introduced and discharged, the first and secondheader tanks being spaced apart from each other by a predetermineddistance; a plurality of flat refrigerant tubes each having oppositeends respectively connected to the first and second header tanks, eachof the refrigerant tubes having channels spaced apart from one anotherin a widthwise direction through which the refrigerant scatter and flow,the channels having a different capacity from each other, the first andsecond header tanks communicating with each other through the channels;and cooling means disposed between the refrigerant tubes, for radiatingheat of the refrigerant flowing along the tubes, wherein widths of thechannels are different from each other and heights of the channels arethe same as each other.
 2. The heat exchanger according to claim 1,wherein each of the refrigerant tubes comprises a refrigerant flow holeof a multi-channel structure having at least two different channelcapacities to allow the refrigerant to scatter and flow.
 3. The heatexchanger according to claim 1, wherein intervals between the channelsare different from each other.
 4. The heat exchanger according to claim1, wherein among the channels, a first channel formed on a front end ofeach of the refrigerant tubes, has a biggest channel capacity, and ann-th channel formed on a rear end of each of the flat tubes has asmallest channel capacity, when the order of the first and the n-th isreferenced by the air flow direction.
 5. The heat exchanger according toclaim 1, wherein the channel capacities of the refrigerant tubes aregradually decreased at a predetermined rate as it goes from a firstchannel formed on a front end of the refrigerant tube to an n-th channelformed on a rear end of the refrigerant tube.
 6. The heat exchangeraccording to claim 5, wherein adjacent channels of each of therefrigerant tubes have a difference in their capacities by apredetermined reduction/increase rate.
 7. The heat exchanger accordingto claim 1, wherein the channels are classified into the predeterminednumber of groups, and capacities of the grouped channels are differentfrom each other.
 8. The heat exchanger according to claim 1, whereinwidths of the channels are gradually reduced at a predetermined rate asit goes from a first channel formed on a front end of the refrigeranttube to an n-th channel formed on a rear end of the refrigerant tube. 9.The heat exchanger according to claim 8, wherein the channel widths ofthe adjacent front and rear channels are reduced at a reduction rate of6%.
 10. The heat exchanger according to claim 8, wherein the channelwidths of the adjacent front and rear channels are reduced at areduction rate of 10%.
 11. The heat exchanger according to claim 1,wherein an inner circumference of the tubes comprises an irregularsurface having a plurality of irregular grooves formed in the innercircumference.
 12. The heat exchanger according to claim 1, wherein thecooling means comprises cooling fins vertically disposed between theflat tubes, and riblets formed in air flow direction on an outer surfacewhere the cooling fins are not formed.
 13. A heat exchanger comprising:first and second header tanks through which refrigerant is introducedand discharged, the first and second header tanks being arranged facingeach other spaced apart from each other by a predetermined distance andhaving at least one separation membrane; a plurality of flat refrigeranttubes each having opposite ends respectively connected between the firstand second header tanks, each of the flat tubes being provided withmulti-channels spaced apart from one another in a widthwise directionand having different channel widths in an exterior air flow directionand having same channel heights, and communicating the first and secondheader tanks with each other to disperse and flow the refrigerant; andheat discharging means including: a plurality of cooling fins disposedin a predetermined shape between the refrigerant tubes; and ribletsprotruded in the air flow direction on an outer surfaces of therefrigerant tubes.
 14. The heat exchanger according to claim 13, whereinthe riblets are shaped in a triangle.
 15. The heat exchanger accordingto claim 13, wherein each of the tubes has an inner circumferencecomprising an irregular surface having a plurality of irregular groovesformed in the inner circumference.
 16. A heat exchanger comprising:first and second header tanks through which refrigerant is introducedand discharged, the first and second header tanks being arranged spacedapart from each other by a predetermined distance; a plurality of flatrefrigerant tubes arranged spaced apart from one another by apredetermined distance and connected between the first and second headertanks, for dispersing and flowing refrigerant, each of the refrigeranttubes having a multi-channel structure including channels spaced apartfrom each other in a widthwise direction and in which a first channel,which is formed on a front end of each tube and first contacts air, hasa biggest channel capacity, and an n-th channel, which is formed on arear end of each tube, has a smallest channel capacity; and cooling finsdisposed between the refrigerant tubes for heat discharge, whereinwidths of the channels are different from each other and heights of thechannels are the same as each other.
 17. A heat exchanger comprising: aplurality of flat refrigerant tubes each having multi-channels includingchannels spaced apart from each other in a widthwise direction and ofwhich widths are gradually reduced by a predetermined reduction ratio asit goes in a direction where exterior air flows and of which heights arethe same, the refrigerant tubes flowing refrigerant between a pair ofheader tanks through the multi-channels; and cooling fins disposedbetween the refrigerant tubes for heat discharge.
 18. The heat exchangeraccording to claim 16, wherein the tubes have an inner circumferencecomprising an irregular surface having a plurality of irregular groovesformed in the inner circumference.
 19. The heat exchanger according toclaim 17, wherein the tubes have an inner circumference comprising anirregular surface having a plurality of irregular grooves formed in theinner circumference.